Composite hollow fiber and related methods and products

ABSTRACT

Described are composite hollow fibers filter membranes that include a porous polymeric hollow fiber support and a filter layer; methods of making the composite hollow fibers and using the composite hollow fibers as a filter membrane; methods of making a filter component or filter from the composite hollow fiber; and filter components and filters that contain the composite hollow fibers as filter membranes.

This application claims the benefit of U.S. Application No. 62/818,984filed on Mar. 15, 2019, which is hereby incorporated by reference in itsentirety.

FIELD

The following description relates to composite hollow fibers that areuseful as filter membranes and that include a porous polymeric hollowfiber support and a filter layer; to methods of making the compositehollow fiber and using the composite hollow fiber as a filter membrane;to methods of making a filter component or filter from the compositehollow fiber; and to filter components and filters that contain thecomposite hollow fibers as filter membranes.

BACKGROUND

A major application of filter membranes is to remove unwanted materialsfrom a flow of a useful fluid. Many gaseous and liquid fluids inindustry are processed using filters, including environmental air,drinking water, liquid industrial solvents and processing fluids,industrial gases used for manufacturing or processing (e.g., insemiconductor fabrication), and liquids that have medical orpharmaceutical uses. Unwanted materials that are removed from fluidsinclude impurities and contaminants such as particles, microorganisms,and dissolved chemical species. Specific examples of impurity removalapplications for filter membranes include their use to remove particlesor bacteria from therapeutic solutions in the pharmaceutical industry,to process ultrapure aqueous and organic solvent solutions for use inmicroelectronics and semiconductor processing, and for air and waterpurification processes.

To perform a filtration function, a filter product includes a filtermembrane that is responsible for removing the unwanted material from thefluid. The filter membrane may, as required, be in the form of a flatsheet, which may be wound (e.g., spirally), or pleated, etc. The filtermembrane may alternatively be in the form of hollow fibers. The filtermembrane can be contained within a housing that includes an inlet and anoutlet, so that fluid that is being filtered enters through the inletand passes through the filter membrane before passing through theoutlet.

Unwanted materials in the fluid are removed from the fluid by beingcaptured by the filter membrane either mechanically orelectrostatically, e.g., by a sieving or a “non-sieving” mechanism, orboth. A sieving mechanism is a mode of filtration by which a particle isremoved from a flow of liquid by retention of the particle at themembrane pore entrance due to mechanical interference of the pore withthe particle movement. In this mechanism at least one dimension of theparticle size is larger than pore size. A “non-sieving” filtrationmechanism is a mode of filtration by which a filter membrane retains asuspended particle or dissolved material contained in a liquid flowingthrough the filter membrane in a manner that is not exclusivelymechanical, e.g., that includes an electrostatic mechanism by which theparticle or dissolved material is electrostatically attracted to andretained at the external or internal surface of the filter membrane(depth filtration).

Filter membranes can be constructed of porous polymeric films that haveaverage pore sizes that can be selected based on the expected use of thefilter, i.e., the type of filtration to be performed using the filter.Typical pore sizes are in the micron or sub-micron range, such as fromabout 0.001 micron to about 10 micron. Membranes with average pore sizeof from about 0.001 to about 0.05 micron are sometimes classified asultrafilter membranes. Membranes with pore sizes between about 0.05 and10 microns are sometimes classified as microporous membranes.

For commercial use, a filter membrane should be of a type that can beefficiently manufactured and assembled into a filter product. Themembrane must be capable of being efficiently produced, and must havemechanical properties such as strength and flexibility that allow thefilter membrane to withstand assembly into the form of a filtercartridge or a filter. In addition to mechanical properties, themembrane should have suitable chemical functionality and microstructurefor high performance filtration. In some applications more than onechemical functionality, microstructure, or pore size is required toachieve high filtration performance. Hence composite membranes having attwo or multiple chemical functionalities are suitable to serve thispurpose.

Various polymers have been identified that can be formed into porous,hollow fiber filter membranes by techniques such thermally induced phaseinversion (TIPS) or non-solvent induced phase inversion (NIPS). Also,various techniques and equipment have been developed for assemblinghollow fiber filter membranes into a final filter product, within ahousing. See, e.g., WO 2017/007683 and U.S. Pat. No. 5,695,702, theentireties of these documents being incorporated herein by reference.

For commercial use, a filter membrane must also exhibit efficient andreliable filtering functionality, e.g., must be capable of efficientlyremoving a high amount of impurities from a continuous flow of fluidthat passes through the filter membrane. Filtering performance isnormally assessed by two parameters including flux and retention. Fluxassesses the rate of fluid flow through a filter or filter membrane, andmust be sufficiently high to reflect that a high level of flow throughthe filter is possible, hence the filter is economically viable.Retention, generally, refers to the amount (in percent) of impuritiesremoved from a flow of fluid through a filter and is an indication offilter efficiency. Membrane flux and retention both significantly dependon the membrane microstructure and pore size, which is commonly measuredby bubble point. A membrane with smaller pores, has a higher bubblepoint and a better sieving retention capability at the expense of lowerflux (assuming the same membrane morphology and thickness); a largerpore size corresponds to a lower bubble point and a lower sievingretention but a higher flux assuming the same membrane morphology andthickness. The non-sieving retention capability of a membrane is a morecomplex property which depends on membrane surface properties (such ascharge) in addition to membrane microstructure and pore size.

One area of major commercial interest for membrane filtration is thecontamination removal from photoresist solutions in the semiconductorindustry. As the semiconductor industry moves towards smaller nodes, thecontamination issue becomes more severe as smaller contaminants couldcause defects in the wafer product and significantly lower theproduction yield. The contaminants in the photoresist fluids couldinclude gels, ions or nanoparticles with organic or inorganic nature.Between the two common geometries for membranes, hollow fiber membranesare of particular interest for contamination removal applications as theoutside-in flow configuration of hollow fiber devices potentiallyprovides faster flush-up time compared with the devices made from flatsheet membranes. Flush-up time is the time required for particle countsin the liquid passed through the filter reach the base line. Thepotentially better flush-up time of hollow fiber devices is because thelumen side of the hollow fiber is not exposed to the environmentcontaminates such as dust and particles during membrane processing,handling and device fabrication, hence more likely to be cleaner. Betterdevice integrity is another potential advantage of hollow fiber devicescompared with pleated flat sheet cartridges as that pleating operationcould create defects on or near the membrane pleat tip especially whenthe membrane material is a brittle polymer.

Due to the nature of organic solvents such as cyclohexanone, n-butylacetate, PGME, and PGMEA used in the photolithography application, thechemical compatibility of a membrane with these solvents is a limitingfactor in membrane material selection for these uses. As a result,solvent compatible polymers including polyethylene and nylon have beenconsidered for preparing hollow membranes used in this application.However, there are major limitations associated with these membranes foruse to meet the highly demanding requirements of contamination removalin the semiconductor industry. The pore size of the polyethylene hollowfiber membranes, which are made by the TIPS process, is normally limitedto pore sizes larger than 40 nm. This limitation is partly due to thenature of the polyethylene solution phase separation and partly due tothe process limitation to cool the extruded fiber quickly. For similarreasons, the achievable degree of asymmetry in the microstructure of theTIPS processed membranes is normally lower than the NIPS processablemembranes. As a result, TIPS processed membranes normally have inferiorflux-bubble point balance compared with the NIPS processed membranes. Inaddition, the non-polar nature of polyethylene polymer results inlimited non-sieving (polar) retention capability of polyethylenecompared with highly polar polymers such as nylon. Unlike polyethylene,nylon membranes have very strong non-sieving retention due to polar andelectrostatic properties of nylon, and these membranes are processableby both NIPS and TIPS processes. However, the slow phase-separatingnature of nylon in the NIPS process makes it difficult to make high BP(small pore size) membranes with good flux. On the other hand, the TIPSprocessing of nylon has similar limitations of the TIPS processedpolyethylene membrane. Overall, there is a need for improved filtrationmembranes that satisfy solvent compatibility, high retention, and goodflux criteria.

SUMMARY

The following description relates to novel composite hollow fibermembranes with high efficiency in contamination removal from photoresistsolutions in the semiconductor manufacturing process, and a process tomake such composite hollow fibers. The membranes uniquely combinedesired sieving properties with strong non-sieving (such aselectrostatic, affinity, phobic) properties to achieve high particleretention and high flux. The invented composite hollow fiber also hasgood mechanical properties for handling, device manufacture, andpressure driven applications.

Fabrication of composite membranes is a useful approach to tailor theproperties of a membrane to achieve high flux, high retention, goodmechanical properties and reasonable cost. For example, a combination ofhigh flux, high retention, and good mechanical properties can beachieved by making a composite membrane having a thin layer with smallpore size (tight layer) on a thicker layer with larger pore size(support layer). In this configuration the high flow resistance of thetight layer is minimized by reducing its thickness while the requiredmembrane mechanical strength is achieved by using a thicker supportlayer with minimal flow resistance due to bigger pore size. Sometimescomposite membrane concepts can be used to lower the cost of membranesmade from expensive polymers by fabricating a thin layer of a functionalexpensive polymer on a thicker support layer. Another useful applicationof composite membranes is where layers with different functionalitiesare required within one membrane to carry out the desired separation.

The development of some types of composite hollow fibers has beenreported. Early developments of such membranes were targeted for gasseparation applications by coating a dense polymer layer on an outersurface of a microporous hollow fiber support. The process forfabrication of such membranes involved coating the outer surface of amicroporous hollow fiber with a polymer solution followed by anannealing step to vaporize the solvent from the coated solution andcreate a dense nonporous layer on the external surface of the hollowfiber. Another example of a method of fabricating a composite membraneinvolves co-spinning two different polymer solution using a dual orificespinneret into a coagulation bath two form a dual layer membrane. Themajor limitation of this method is the difficulty to tailor theproperties of each layer independently as the phase separation of onelayer affects the rate of phase separation of the other layer, hence itsproperties. Also, it is sometimes impossible or very complicated to makea dual layer hollow fiber membrane with one layer out of a NIPSprocessable polymer and another layer out of a TIPS processable one. Forexample, to make a polyethylene (PE)-polyethersulfone (PESU) compositehollow fiber by this method, the high temperature (around 150 C) of thepolyethylene solution required for TIPS processing increases thespinneret temperature and subsequently the processing temperature of thePESU solution. This could negatively affect the phase separation ofpolyethersulfone layer as PES polymer solution tends to phase separateat high temperatures. Therefore, the PES solution may phase separateinside the spinneret before entering the coagulation bath. Thisphenomenon could hinder the optimal control of the PES layer properties.

Applicant has now discovered novel hollow fiber filter membraneconstructions that can exhibit useful or advantageous filteringperformance properties, including high flux combined with relativelyhigh bubble point (small pore size) and good retention. The performancecompares well or shows substantial improvement relative to previous andcurrent commercial hollow fiber filter membrane products.

As described herein, hollow fiber filter membranes are made in compositeform. The composite includes a porous, polymeric hollow fiber support,with a porous filter layer disposed on the hollow fiber support. Thehollow fiber support functions as a support structure on which thefilter layer is positioned. The hollow fiber support may also be capableof functioning as a filter, but is not required to function as a filterto remove unwanted material from a flow of liquid that is passed throughthe composite hollow fiber membrane. Depending on the type and size ofunwanted material (contaminant) being removed from a fluid that passesthrough the composite filter membrane, and depending on the physicalproperties (e.g., pore size) and chemical makeup of the hollow fibersupport, the hollow fiber support may be effective to remove unwantedmaterial either by a sieving or a non-sieving mechanism. Alternatively,the hollow fiber support is not required to provide a substantialfiltering effect, and a majority of the filtering performance of thecomposite may be provided by the filter layer.

The filter layer is porous, and performs a function of filtering, i.e.,removing unwanted material from, a flow of liquid that is passed throughthe composite hollow fiber membrane. The filter layer can preferably bein the form of a thin, porous layer of filter layer polymer that islocated on an exterior side of the hollow fiber support. The poroushollow fiber support includes a matrix of pores that extend through athickness of the hollow fiber support. The composite, therefore,includes a layer of the hollow fiber support, and the filter layer.

In certain embodiments, the hollow fiber support may have pores that arerelatively larger than pores of the filter layer, and may be relativelythicker than the filter layer. In these example composites, therelatively larger pore size of the larger (thicker) hollow fiber supportcauses a reduced level of resistance of flow through the hollow fibersupport (and greater flow with a lower flow time) relative to acomparable support that would have smaller pores. The filter layer,which is thinner but has a relatively smaller pore size, is highlyeffective as a filter, to remove unwanted material from a fluid flow,but because it is relatively thin, still allows for a useful oradvantageously high volume of flow through the composite.

The filter layer is made of polymer (referred to as “filter layerpolymer”) that is solution processable, meaning that the filter layerpolymer can be dissolved in solvent to form a polymer solution that canbe used to coat the filter layer polymer onto the hollow fiber support.By one example, a layer of polymer solution that contains filter layerpolymer dissolved in solvent can be coated as a layer of coated polymersolution onto outer portions of a hollow fiber support; subsequently,the coated polymer solution can be exposed to a non-solvent (meaning aliquid in which the dissolved filter layer polymer is substantiallyinsoluble), and the filter layer polymer will precipitate (e.g.,coagulate) to form a layer of precipitated (coagulated) filter layerpolymer on the outer surface of the hollow fiber support.

The filter membrane may be used to filter (i.e., remove material from) aliquid that must be used at a high purity level in a commercial orindustrial process. The process may be any that requires a high purityliquid material as an input, with non-limiting examples of suchprocesses including processes of preparing microelectronic orsemiconductor devices, a specific example of which is a method offiltering a liquid process material (e.g., solvent or solvent-containingliquid) used for semiconductor photolithography or cleaning and etchingprocesses. Examples of contaminants present in a process liquid orsolvent used for preparing microelectronic or semiconductor devices mayinclude metal ions dissolved in the liquid, solid particulates suspendedin the liquid, and gelled or coagulated materials (e.g., generatedduring photolithography) present in the liquid.

In one aspect, a composite hollow fiber filter membrane that includes: apolymeric, microporous, hollow fiber support having an outer surface, aninner surface, a thickness extending between the outer surface and theinner surface, and micropores; and a porous polymeric filter layercomprising coagulated polymer contacting the outer surface. In someembodiments, the porous polymeric filter layer penetrates not more thanpartially into the thickness of the hollow fiber support. In otherembodiments, the porous polymeric filter layer penetrates substantiallyinto the thickness of the hollow fiber support.

Another aspect relates to a method of preparing a composite hollow fiberfilter membrane comprising a hollow fiber support and a porous polymericfilter layer. The method includes: placing a polymer solution coating onan outer surface of a polymeric, microporous, hollow fiber support, thepolymer solution comprising polymer dissolved in solvent; and contactingthe polymer solution coating with coagulation solution to causedissolved polymer of the polymer solution coating to form a layer ofcoagulated polymer on the outer surface, the layer of coagulated polymercontacting the outer surface and penetrating not more than partiallyinto a thickness of the hollow fiber support.

Yet another aspect relates to a filter that includes a composite hollowfiber filter membrane comprising: a polymeric, microporous, hollow fibersupport having an outer surface, an inner surface, a thickness extendingbetween the outer surface and the inner surface, and micropores; and aporous polymeric filter layer comprising coagulated polymer contactingthe outer surface and penetrating not more than partially into thethickness of the hollow fiber support.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a schematic diagram of a system for coating a filter layerof the invention onto a hollow fiber support to produce a composite asdescribed.

FIG. 1B shows a schematic cross-sectional view of a composite hollowfiber as described.

FIGS. 2 and 3 show example embodiments of filter and components of afilter that include a composite hollow fiber filter membrane of thedescription.

The figures are schematic and are not necessarily to scale.

DETAILED DESCRIPTION

Applicant has identified novel composite hollow fiber filter membranesand methods for preparing composite hollow fiber filter membranes (alsosometimes referred to herein as “composite membranes,” “composite filtermembranes,” “composite,” or the like). The composite filter membranesinclude a hollow fiber support and a filter layer disposed on the hollowfiber support. The hollow fiber support may perform a sieving or anon-sieving filtration function, while performing the function ofmechanically supporting the composite during use and providing alocation for the filter layer within a hollow fiber filter cartridge ora hollow fiber filter membrane. The hollow fiber support is not requiredto function as a filtering component of the composite, but can provideuseful support and useful physical and mechanical properties to thecomposite, and good flow properties, to allow fluid to flow through thesupport and through the filter layer during use of the composite as afilter. The filter layer performs the function of filtering (i.e.,removing unwanted material from) a flow of fluid that is passed throughthe composite filter membrane. The composite can exhibit a useful oradvantageous combination of flow properties and filtering performance.

The hollow fiber support (also referred to herein as simply the“support”) is a polymeric hollow fiber material that is porous, and thatcan effectively support the filter layer so that fluid can be passedthrough the filter layer, e.g., when the composite hollow fiber filtermembrane is included in a filter cartridge or a filter. The hollow fibersupport is polymeric, porous, and sufficiently rigid yet flexible toallow for its use as a supportive component of a composite hollow fibermembrane as described. The support has features such as porosity, poresize, thickness, and composition (i.e., polymeric makeup), that togethercontribute to the properties of the support. The support should besufficiently porous, and with suitable pore size, to allow for liquidfluid to pass through the support at a flow rate that is sufficient forthe composite filter membrane to be used in a commercial filteringapplication. In certain embodiments of the composite, in addition tofunctioning as a support, the hollow fiber support can also be effectiveas a filter to remove unwanted material from a flow of fluid either by asieving or a non-sieving filtering mechanism. In these examplecomposites, the physical properties (e.g., pore size, thickness) and thechemical composition of the hollow fiber support, or both, can beeffective for filtration by a sieving mechanism, a non-sievingmechanism, or both.

A hollow fiber support can have any porosity that will allow the poroussupport to be effective as described herein, to allow a suitable flowrate of liquid to pass through the support and through a filter layersituated on the support, and if desired to allow the hollow fibersupport to perform a filtering function by a sieving or a non-sievingfiltering mechanism. Examples of useful hollow fiber supports can have aporosity of up to 90 percent, e.g., a porosity in a range from 60 to 90,e.g., 65 to 80 percent. As used herein, and in the art of porous bodies,a “porosity” of a porous body (also sometimes referred to as “voidfraction”) is a measure of the void (i.e. “empty”) space in the body asa percent of the total volume of the body, and is calculated as afraction of the volume of voids of the body over the total volume of thebody. A body that has zero percent porosity is completely solid.

The size of the pores of the hollow fiber support (i.e., the averagesize of pores throughout the hollow fiber support) can be of a sizethat, in combination with the porosity, thickness, and inner and outerdiameter dimensions, provides for desired flow of liquid fluid throughthe hollow fiber support, provides a porous surface to which the polymerfilter layer can be adhered, and if desired allows the hollow fibersupport to perform a filtering function by a sieving or a non-sievingfiltering mechanism.

A pore size that will be useful for a particular hollow fiber support,e.g., in a specific composite membrane, can depend on factors such as:the thickness of the hollow fiber support; the thickness, porosity,composition, and pore size of the filter layer; the degree to which thehollow fiber support will perform as a filter to remove unwantedmaterials from a flow of fluid; the desired flow properties andfiltering properties of the composite; and features of the method bywhich the filter layer is deposited (e.g., coated) onto the hollow fibersupport including viscoelastic properties of the coated polymersolution. For certain presently understood examples of immersion coatingmethods useful (as described herein) to place a filter layer on a hollowfiber support, example pore sizes of a hollow fiber support may be in arange from about 30 nanometers, 50 nanometers, 0.05 microns, up to 10microns, e.g., of sizes sometimes classified as “microporous,”“ultraporous,” or “nanoporous.” For purposes of the present description,the term “microporous” is sometimes used to refer to pores within any ofthese size ranges, including microporous and sub-microporous sizes, as away of distinguishing from materials having larger pore sizes, i.e., todistinguish over materials that are considered to be “macroporous.”Examples of average pore sizes of a hollow fiber support may be at least30 nanometers, at least 50 nanometers, or at least 0.1 or 0.5 microns,and up to about 4, 6, 8, or 10 microns.

During coating of the polymer solution onto the support, a specificdegree of penetration may be desired. The degree of penetration may beany that is useful, either a high or a low degree of penetration. If apore size of the support is large, a polymer solution applied to thesupport (for placing the filter layer) will tend to penetrate into thepores of the support to a relatively greater depth (as compared topenetration into a support with smaller pore size), potentially a depththat is either not necessary or not desired. If pore size of the supportis too small, the pores can become closed, clogged, blocked, or filled,by the polymer solution in a manner that would unacceptably inhibit orprevent flow of liquid through some or all of the pores during use,producing a substantial reduction in the ability of a liquid to flowthrough the hollow fiber support during use as a component of acomposite filter membrane, e.g., can undesirably and unacceptably reduceflux. Based at least on differences in pore size, a tubular braidedhollow membrane, e.g., of the type described in U.S. Pat. No. 5,472,607,may be unsuitable or non-preferred as a hollow fiber support for use ina composite hollow fiber membrane as described.

A hollow fiber support can have thickness, inner diameter, and outerdiameter dimensions that are effective for the support to function as asupport component of a composite filter membrane as described. Examplesof useful wall thicknesses of a hollow fiber support may be in a rangefrom 25 to 250 microns, e.g., from 30 to 150 or 200 microns. Examples ofuseful inner diameters of a hollow fiber support may be in a range from300 to 1000 microns, e.g., from 400 to 700 or 900 microns. Examples ofuseful outer diameters of a hollow fiber support may be in a range from500 to 1500 microns, e.g., from 600 to 1200 or 1300 microns.

A hollow fiber support may be made of any polymer that is useful to forma hollow fiber for use as a composite filter membrane as describedherein. The support should be chemically resistant to (e.g., notchemically degraded by) liquids that will be passed through the supportwhen used as a component of a composite filter membrane in a filteringstep. Useful examples include polymers that have been used or that arefound to be useful as hollow fiber filter membranes for filtering fluidsused in semiconductor and microelectronic processing (e.g., solvent orprocess fluids), examples of which are known and include fluoropolymers(e.g., Teflon™), polyethylene, polypropylene, nylons that are compatiblewith photolithography solvents used in semiconductor fabrication. If theexpected us of the filter membrane is in the semiconductor dilute wetetch and clean process, the choice of hollow fiber support may be afluoropolymer or a sulfone polymer hollow fibers such as Teflon. Theseexamples contemplate homopolymers and co-polymers of polyolefins such aspolypropylene and polyethylene, particularly ultrahigh molecular weightpolyethylene (UPE), nylons (e.g., polyamides), and other known polymermaterials. The hollow fiber support polymer can preferably (but notnecessarily) be compatible with a solvent used for processing the filtercoating layer, examples of which include NMP, DMF, DMAc and Acetone.Fluoropolymers such as Teflon, polyethylene, polypropylene and nylon areexamples of such polymers.

For a hollow fiber support that will be used and effective for filteringby a non-sieving method, certain polymers can be useful or preferred.Examples of polymers that may be useful as part of a filter membrane,for non-sieving filtering functionality, include polyamides (e.g.,nylons); polyimides; polyamide-polyimides; surface treated versions ofpolyamides, polyimides, or polyamide-polyimides. A desired polymer maybe selected base on the type of contaminant that is being removed. Forexample, nylon polymer may be effective to remove organic gels ordissolved metal contaminants from an organic solvent. A polymer thatincludes anionic (negatively charged) surface groups may be effective toremove cationically (positively) charged contaminants that are dissolvedor suspended in a liquid.

In certain examples, a hollow fiber support can be made of ultrahighmolecular weight polyethylene (“UPE”), which is generally understood tomean polyethylene polymer having a molecular weight of at least1,000,000 Daltons. The term “polyethylene” refers to a polymer that has,in part or substantially, a linear molecular structure of repeating—CH2—CH2— units. Polyethylene can be made by reacting monomercomposition that includes monomers that comprise, consist of, or consistessentially of ethylene monomers. Thus, a polyethylene polymer may be apolyethylene homopolymer prepared by reacting monomers that consist ofor consist essentially of ethylene monomers. Alternatively, apolyethylene polymer may be a polyethylene copolymer prepared byreacting a combination of ethylene and non-ethylene monomers thatinclude, consist of, or consist essentially of ethylene monomers incombination with another type of monomer such as another alpha-olefinmonomer, e.g., butene, hexene, or octane, or a combination of these; fora polyethylene copolymer, the amount of ethylene monomer used to producethe copolymer, relative to non-ethylene monomers, can be any usefulamount, such as an amount of at least 50, 60, 70, 80, or 90 percent (byweight) ethylene monomer per total weight of all monomers (ethylenemonomer and non-ethylene monomer) in a monomer composition used toprepare the ethylene copolymer.

As used herein, a composition that is said to “consist essentially of” aspecified composition, ingredient, or a specified combination ofingredients, means a composition that contains the specifiedcomposition, ingredient, or a specified combination of ingredients andnot more than an insubstantial amount of other ingredients, e.g., notmore than 3, 2, 1, 0.5, or 0.1 weight percent of any other materials.Monomers that consist essentially of ethylene monomers refers to acomposition that contains ethylene monomer and not more than 3, 2, 1,0.5, or 0.1 weight percent of any other monomers, based on total weightof all monomers in the composition. Monomers that consist essentially ofethylene and alpha-olefin monomers refers to a composition that containsethylene and alpha-olefin monomers and not more than 3, 2, 1, 0.5, or0.1 weight percent of any other monomers, based on total weight of allmonomers in the composition.

The hollow fiber support maybe prepared in any known or future usefulfashion to produce a hollow fiber support having properties asdescribed. Examples of known methods for preparing hollow fiberthermally induced phase separation (TIPS) and immersion precipitationmethods (also called non-solvent induced phase separation of NIPS).

The composite hollow fiber filter membrane includes a filter layerprovided on the hollow fiber support at a location and in an amount thatallow for the filter layer to function as a filter to remove unwantedmaterial from a flow of fluid that passes through the composite. Thefilter layer is porous, relatively thin compared to the thicknessdimension of the hollow fiber support, and is preferably coated onto anouter porous surface of the hollow fiber support in a manner thatmechanically secures the filter layer to the outer porous surfacewithout substantially or unduly covering, blocking, or filling pores ofthe outer porous surface.

The composition and the physical features (such as porosity and poresize) of the filter layer are independent from the composition andphysical features of the hollow fiber support. The primary function ofthe filter layer is to filter (i.e., remove unwanted material from) aliquid fluid as the liquid fluid flows through the filter layer. Toperform this function, the filter layer should be situated at a locationto allow liquid to flow through the filter layer while flowing throughthe support. For example the filter layer can be positioned at an outerporous surface of the support. The filter layer should be evenlydistributed over the outer porous surface and should be distributed oversubstantially the entire area of the outer porous surface, to beeffective as a filter. The filter layer can have of any thickness,porosity, and pore size (average) that will be useful to effectivelyperform the filtering function by a sieving mechanism, a non-sievingmechanism, or both. Generally, a filter layer can have a substantiallysmaller thickness relative to the support (i.e., the filter layer issubstantially thinner than the support). In various example embodiments,a filter layer may have a smaller pore size relative to the pore size ofa support, or may have a pore size that is about the same as or largerthan the pore size of the support.

An example filter layer can have any porosity that will allow the filterlayer to be effective as a filter layer. Examples of useful filterlayers can have a porosity of up to 90 percent, e.g., a porosity in arange from 60 to 85, e.g., 65 to 80 percent.

The size of the pores of the filter layer (i.e., the average size ofpores throughout the filter layer) can, in combination with theporosity, thickness, and composition of the filter layer, be any sizethat is effective to provide for a useful or advantageous level offiltering functionality (e.g., as measured by retention) when liquid ispassed through the composite filter membrane, while also allowing for arate of flow of the fluid through the filter layer (and composite filtermembrane) that is sufficiently high for the composite filter membrane tobe commercially useful.

In particular embodiments of a composite as described, a filter layercan have smaller pores relative to the hollow fiber support. Accordingto these embodiments, the resistance to flow of fluid though the filterlayer will be greater (per thickness) than the resistance to fluid flowthrough the larger-pore-sized support (per thickness). Preferred suchexample composites may also include a thicker hollow fiber support withgood flow properties, and the relatively thinner filter layer with goodfiltering properties to produce a composite that exhibits anadvantageous combination of good flow properties through the compositealong with highly useful or advantageously high filtering performanceprovided by the relatively thin filter layer. The composite also hasuseful mechanical properties including desired levels of flexibility andrigidity, with the filter layer being effectively secured to thesupport, and both the support and the filter layer being not excessivelybrittle or breakable.

A useful pore size for a filter layer can depend on factors such as: thethickness, porosity, and composition of the filter layer; the desiredflow properties and filtering performance properties (e.g., retention)of the composite filter membrane; and features of the method by whichthe filter layer is deposited (e.g., coated) onto the hollow fibersupport. For certain presently useful examples of placing a filter layeron a hollow fiber support by immersion coating, example pore sizes of afilter layer may be from at least 1 nanometer, e.g., at least 10, 30, or50 nanometers, or 0.05 microns, up to 2, 4, 6, or 8 microns.

A filter layer can have thickness that will result in effectivefiltering and flow performance as described herein. Additionally, thethickness of the filter layer should result in the filter layerpenetrating into and contacting internal surfaces of the porous hollowfiber support to mechanically secure the filter layer to the hollowfiber support. The filter layer can partially or fully penetrate intothe hollow fiber support to thereby become mechanically adhered andwell-anchored to the support, without causing a substantial amount ofclogging or filling of the pores of the hollow fiber support. Examplesof useful thicknesses of a filter layer may be in a range from 5 to 40microns, e.g., from 10 to 20 microns (not including the distance towhich the filter layer penetrates into the support). Examples of thedistance to which the filter layer penetrates into the thickness of thehollow fiber support can be less than 2 microns or less than 1 micron,although distances greater than these can also be useful, potentiallyincluding a filter layer that penetrates completely into the supportlayer.

To be effective for filtering a liquid, the filter layer can be made ofa polymer (a “filter layer polymer”) that is resistant to solvents andother chemical materials that will be present in a liquid that will beprocessed using the filter layer. Filter layer polymers that arepresently understood to be useful according to the present descriptioninclude those that are chemically resistant to (e.g., not chemicallydegraded by) liquids used in semiconductor and microelectronicprocessing (e.g., solvent or process fluids). Examples may generallyinclude polymers that are useful (at present or in the future) forpreparing hollow fiber filter membranes used for filtering fluids forsemiconductor and microelectronic processing (e.g., solvent or processfluids), with specific examples including polyimides, polyamides,polyamide-imides, polysulfone family polymers e.g., homopolymers andco-polymers of polyimides, polyamides, polysulfone, polyethersulfone,and polyphenylsulfone.

Polyamides are a class of well-known polymers that include nylons.Polyamides are chemically considered to be polymers that includemultiple repeating carbon-carbon organic polymeric backbone unitsseparated by repeating amide linkages. Polyamides can be prepared byreacting monomers or reactive ingredients that include functional groupscapable of combining to form a polymer backbone having repeating amidelinkages. Examples of a combination of monomers useful to preparepolyamides include di-amine monomers and di-carboxylic acid monomers.Example polyamides include copolymers and terpolymers prepared bypolymerizing a combination of two or three diamine and dicarboxylic acidmonomers. Certain presently-preferred polyamides include nylons such asNylon 6 and Nylon 6,6.

Polyimide (sometimes abbreviated PI) is a polymer that includes imidelinkages in a carbon-carbon polymer backbone. Polyimide polymers may be“pure” polyimides that contain imide linkages but no ester or amidelinkages, or may alternately contain other non-carbon-carbon linkagessuch as ester linkages or amide linkages. Certain presently-preferredpolyamides include those referred to as P84 and Matrimid polyimides.

Polyamide-polyimide polymers (sometimes abbreviated as PAI) includeamide and imide linkages. Some specific examples of polyamide-imidepolymers include those prepared from an aromatic diamine and aromaticacid chloride anhydride (acid chloride route), while others may beprepared from aromatic diisocyanate and anhydride (diisocyanate route).Example of commercial polyamide-imides are polymers sold by SolvaySpecialty Polymers, under the trademark Torlon.

Some polyimide or polyamide polymers may be mechanically brittle orinflexible if included in a filter membrane (or other structure) at arelatively high thickness, e.g., if the polymer were used by itself toform an entire thickness of a hollow fiber membrane. Some polyimides, ifused alone to form an entire thickness of a porous hollow fibermembrane, e.g., of a thickness up to or greater than 30 or 50 microns inthickness, will tend to be mechanically brittle or fragile to an extentthat would prevent the hollow fiber membrane from being commerciallyuseful. As determined by Applicant, however, thinner layers these ofthese polymers, such as in the form of a thin filter layer of acomposite membrane, as described, can exhibit mechanical properties(including flexibility and reduced brittleness) that allow the polymersto be placed onto a support and processed and formed into a filter, andused as a filter, without being mechanically unsuitable.

For processability, a preferred filter layer polymer can be one that iscapable of being effectively (and preferably efficiently) placed by auseful coating method on an outer porous surface of a support asdescribed. Preferred filter layer polymers are capable of beingdissolved in solvent to form a polymer solution that can be coated ontoa porous outer surface of a hollow fiber support and then precipitatedfrom the polymer solution onto surfaces of the outer porous surface toform an effective filter layer as described. Presently useful andpreferred filter layer polymers can be dissolved in solvent to form apolymer solution that can be coated onto an outer porous surface of ahollow fiber membrane using an annular die, then coagulated by animmersion precipitation method to form a useful filter layer. The amount(e.g., thickness) and placement of the filter layer can be sufficient toallow the filter layer to show highly effective filtering performance(e.g., as measured by retention) as the filter layer of a compositehollow fiber filter membrane, while still allowing for a desirably highlevel of flow of liquid through a composite hollow fiber filter membraneas described.

A useful filter layer polymer can be provided as a coating on the porouspolymeric film coating by any useful coating technique, such as byprecipitation coating, preferably from a polymer solution in which thefilter layer polymer is dissolved in solvent. Preferred filter layerpolymer is, therefore, solvent processable and capable of beingdissolved in solvent for coating onto a support such as a hollow fibersupport. The solvent may be any useful solvent, with examples includingNMP (n-methyl pyrrolidone), DMF (N,N-dimethylformamide), andN,N-dimethylacetamide (DMAC). The solvent may preferably contain nowater or not more than a low amount of water, such as not more thanabout 2, 1, or 0.5 weight percent water. The polymer solution may alsocontain a non-solvent such selected from non-limiting examples thatinclude an alcohol, an acid, an ether, etc. Also, in addition tooptional nonsolvent, the polymer solution may contain other additivessuch pore forming agents such as polyvinylpyrrolidone (PVP),polyethylene glycol (PEG), etc.

The polymer solution may contain any effective amount of solvent anddissolved filter layer polymer. Example polymer solutions may containany effective amount of filter layer polymer, such as an amount in arange from 5 to 30 percent by weight, e.g., from 10 to 20 (or 25) weightpercent filter layer polymer with the balance being solvent (e.g.,organic solvent as described herein optionally in combination withnon-solvent and pore forming agent).

The filter layer polymer may be but is not necessarily, and is notrequired to be, curable or reactive with itself, such as to becrosslinked. As a result, the polymer solution that contains the filterlayer polymer dissolved in solvent is not required to contain, and mayoptionally exclude (e.g., contain less than 0.05, 0.01, or 0.005 weightpercent) any chemical ingredient that is useful to produce a curingreaction of the coated filter polymer, such as a crosslinker, catalyst,or initiator.

The composite hollow fiber filter membrane includes the hollow fibersupport and the filter layer. While additional layers or materials mayoptionally be included, the described composite does not require and mayin certain embodiments preferably exclude other layers, coatings, ormaterials. For example, certain example composite membranes of thepresent description do not require and may preferably exclude anintermediate coating or layer that would be located between the poroussupport and the filter layer, such as a primer layer or coating disposedon the outer porous surface of the support for the purpose of improvingadhesion of the filter layer to the support. In such embodiments thefilter layer can be disposed directly onto the outer porous surface ofthe support.

In an example of a presently-preferred method for preparing a hollowfiber composite as described, a filter layer may be formed onto a hollowfiber support by forming a polymer solution that contains the filterlayer polymer and placing the filter layer polymer on an outer poroussurface of the hollow fiber support by an immersion precipitation orthermally-induced phase inversion coating technique. By immersionprecipitation, generally, polymer solution that contains dissolvedpolymer in solvent is cast on a supporting layer and then submerged in acoagulation bath that contains “nonsolvent,” meaning a liquid in whichthe polymer is not substantially soluble. Due to the solvent andnonsolvent exchange, the polymer precipitates from the polymer solutiononto the supporting layer. The polymer must be highly soluble in thesolvent of the polymer solution and substantially insoluble in the“non-solvent” so that the polymer precipitates or coagulates uponcontact with the non-solvent (e.g., aqueous liquid) of the coagulationbath.

In some embodiments for preparing a hollow fiber composite as described,filter polymer can be dissolved in solvent to form a polymer solutionthat can be applied to an outer porous surface of a hollow fiber supportby an immersion precipitation method. A general method includes one ormore steps that include: forming or otherwise providing a polymersolution that includes the filter layer polymer; applying the polymersolution to an outer porous surface of the hollow fiber support; causingthe filter layer polymer of the polymer solution to precipitate (e.g.,coagulate) out of solution and onto the outer porous surface of thehollow fiber support; and drying the precipitated filter layer polymerto form a composite that includes the filter layer coated on the outerporous surface of the hollow fiber support.

An example of such a method can include the use of an annular die toguide and support the un-coated hollow fiber support, moving through theannular die, while polymer solution passes through the annular die andonto an outer porous surface of the hollow fiber support. An annular dieincludes an inner cylindrical support and an outer cylindrical support,aligned concentrically to form an annular opening having a substantiallyuniform size (width) between an outer surface of the inner cylindricalsupport and an inner surface of the outer cylindrical support. The innercylindrical support also defines a circular opening that is sized tocontain and guide movement of the hollow fiber support. As the hollowfiber support is being passed through the annular die (e.g., pulledthrough the die in a vertically downward direction) a flow of polymersolution is passed through the annular opening to become coated onto anouter surface of the hollow fiber support. The diameter of the circularopening is sufficient for a desired fit of the hollow fiber supportwithin the circular opening, e.g., to allow the hollow fiber support topass through the circular opening at a desired speed. The size (width)of the annular opening can be effective to place a coating of thepolymer solution, having a desired thickness, onto the outer surface ofthe hollow fiber support as the support passes through the circularopening.

Any effective coating equipment, conditions and processing parametersmay be used, including, for example, the draw speed of the support, theflow rate of polymer solution, and the relative size of the annular diecompared to the support diameter. The flow rate of the polymer solutionand the speed of the hollow fiber support passing through a die maydetermine the thickness of the coating filter layer.

According to certain examples of this type of coating technique, thecoated polymer solution (placed onto the hollow fiber support by theannular die) may optionally be exposed to air after the coating step(after passing through the annular die) and before the polymer iscontacted with the non-solvent of the coagulation bath. Exposure to airafter coating and before entering the coagulation bath is not necessary,but can allow partial drying of the coated polymer before contact withthe coagulation bath. While not necessary or required, exposure to airbefore the coagulation bath may be useful to obtain more penetration ofthe coated polymer layer into the hollow fiber support to achieve bettermechanical interlock between the support and the coated layer. If theair-gap is too large, however, the penetration may be too great and themembrane flux could be negatively affected. Alternately, the air-gap maybe useful to achieve a particular microstructure in the coated layer byevaporation of solvent during exposure to air, which may result in somedegree of some phase separation. If an air-gap is present, the amount oftime to which the coated polymer solution is exposed to air before beingcontacted with the non-solvent can be as desired, e.g., less than 2seconds, less than 1 second, or less than 0.5 second.

Referring to FIG. 1A, illustrated is a portion of an immersion coatingsystem that is effective for preparing an example composite hollow fiber70 as described. FIG. 1B shows a cross-sectional view of compositehollow fiber 70.

System 10 includes hollow fiber support 20, polymer solution 30, andannular die 34. A source (not shown) of hollow fiber support 20, such asa spool or bobbin wound with a continuous length of hollow fiber support20, is located to allow hollow fiber support 20 to be supplied to system10. One or more rollers (also not shown) can be used to guide hollowfiber support 20 to and through the different components and locationsof system 10.

Polymer solution 30 is supplied to annular die 34, which includes innercylindrical support 36, outer cylindrical support 38, circular opening40 (defined by an inner surface of inner cylindrical support 36), andannular opening 42 (between inner cylindrical support 36 and outercylindrical support 38). Hollow fiber support 20 is threaded throughcircular opening 40 and is advanced through circular opening 40 (in adownward direction in FIG. 1A) while a flow of polymer solution 30 isdispensed through annular opening 42. A syringe or a pump (not shown)causes polymer solution 30 to flow at a steady rate from a bottom ofannular opening 42, under a desired level of pressure and flow, to placea continuous and substantially uniform coating of polymer coating 50 (inun-coagulated form) on an outer surface of support 20.

Located vertically below annular die 34 is coagulation bath 60,containing non-solvent 62. Hollow fiber support 20 exits annular die 34with un-coagulated polymer coating 50 present at the outer poroussurface of hollow fiber support 20. To cause the dissolved polymer ofpolymer coating 50 to coagulate and form a filter layer (thin porouscoating layer) 64 on the outer surface of hollow fiber support 20, thehollow fiber support 20 with un-coagulated polymer coating 50 nextcontacts non-solvent 62 of coagulation bath 60. Non-solvent 62 contactspolymer coating 50 and interacts with the solvent and dissolved filterlayer polymer of polymer coating 50 to cause the dissolved filterpolymer to precipitate out of solution (e.g., coagulate) to form a layerof filter polymer on the outer surface of support 20. The result iscomposite hollow fiber 70 made of support 20, with filter layer 64(un-dried, as illustrated) coated on an outer porous surface thereof.

Optionally, and as illustrated, support 20 with un-coagulated polymercoating 50 passes through air-gap 52 after exiting annular die 34 andbefore contacting non-solvent 62 of coagulation bath 60. Upon enteringcoagulation bath 60, non-solvent 62 causes polymer solution 50 to phaseseparate and form porous coating layer (filter layer) 64 compositehollow fiber 70. In other example embodiments, no air-gap is presentbetween annular die 34 and non-solvent 62, and the phase separationoccurs inside the coagulation bath immediately polymer coating 50 (onsupport 20) exists annular die 34.

In some examples of the coating method, the polymer solution (as polymercoating 50) at least partially penetrates into pores of the outer poroussurface of the hollow fiber support 20. Upon coagulation of the filterpolymer of polymer coating 50, mechanical interlocking occurs betweenthe coated (coagulated) filter layer 64 and the outer porous surface ofthe hollow fiber support 20. In some embodiments, the degree (depth) ofpenetration of polymer solution 30 into hollow fiber support 20 at theouter porous surface is sufficiently small so that the fluid transportresistance through composite 70 remains sufficiently low to allowcomposite 70 to function as a useful filter membrane.

As one or more optional subsequent steps, a washing tank, heating step,drying step, annealing step, godet rolls, or winding section, may beused to further handle or process composite 70. For example, after thephase separation (coagulation) step, composite hollow fiber 70 can beguided through a washing tank to extract residual solvent. Subsequently,the washed (still wet) composite may be collected on a roll, optionallybefore or after a post-processing annealing or drying step.

A composite filter membrane as described can be useful to remove one ormore contaminants from a liquid by passing the liquid through the filtermembrane to produce a filtered (or “purified”) liquid (sometimesreferred to as a “permeate”). The filtered liquid will contain a reducedlevel of a contaminant compared to a level of the contaminant present inthe liquid before the liquid is passed through the composite filtermembrane. As desired to maintain the placement of the filter layer on anouter surface of the support, liquid can be flowed in a direction offlow from the outside surface to the inner hollow opening of thecomposite; i.e., liquid may be passed from an exterior of the hollowcomposite, first through the filter layer at an outside surface of thecomposite, next through the hollow fiber support, and then enter andflow along the hollow interior of the composite.

A composite as described can provide a useful, desirable, oradvantageous combination of physical properties, including performance(filtering performance as measured by “retention”), pore size or bubblepoint (related to pore size), flow, and mechanical properties(flexibility and durability or reduced fragility).

A level of effectiveness of a composite filter membrane in removingunwanted material (i.e., “contaminants”) from a liquid can be measured,in one fashion, as “retention.” Retention, with reference to theeffectiveness of a filter membrane (e.g., a composite filter membrane asdescribed), generally refers to a total amount of an impurity (actual orduring a performance test) that is removed from a liquid that containsthe impurity, relative to the total amount of the impurity that was inthe liquid upon passing the liquid through the filter membrane. The“retention” value of a filter membrane is, thus, a percentage, with afilter that has a higher retention value (a higher percentage) beingrelatively more effective in removing particles from a liquid, and afilter that has a lower retention value (a lower percentage) beingrelatively less effective in removing particles from a liquid.

Particle retention can be measured as by measuring the number of testparticles removed from a fluid stream by a membrane placed in the fluidstream. By one method, particle retention can be measured by passing asufficient amount of an aqueous feed solution of 0.1% Triton X-100,containing 8 ppm polystyrene particles having a nominal diameter of 0.03microns (available from Duke Scientific G25B), to achieve 1% monolayercoverage through the membrane at a constant flow of 7 milliliters perminute, and collecting the permeate. The concentration of thepolystyrene particles in the permeate can be calculated from theabsorbance of the permeate. Particle retention is then calculated usingthe following equation:

${{particle}\mspace{14mu} {retention}} = {\frac{\lbrack{feed}\rbrack - \lbrack{filtrate}\rbrack}{\lbrack{feed}\rbrack} \times 100{\%.}}$

“Nominal diameter,” as used herein, is the diameter of a particle asdetermined by photon correlation spectroscopy (PCS), laser diffractionor optical microscopy. Typically, the calculated diameter, or nominaldiameter, is expressed as the diameter of a sphere that has the sameprojected area as the projected image of the particle. PCS, laserdiffraction and optical microscopy techniques are well-known in the art.See, for example, Jillavenkatesa, A., et al.; “Particle SizeCharacterization;” NIST Recommended Practice Guide; National Instituteof Standards and Technology Special Publication 960-1; January 2001.

In preferred embodiments of composite membranes as described, acomposite membrane can exhibit a retention that exceeds 90 percent formonolayers coverages of 0.5%, 1.0%, 1.5%, and 2.0%, and may also exceed95 percent for monolayers coverages of 0.5% and 1.0%. With this level ofretention, these examples of the inventive composite membranes exhibit ahigher retention level as compared to many currently commercial filtermembranes, such as comparable flat sheet and hollow fiber filtermembranes made of UPE. These example composite membranes also allow foruseful, good, or very good rates of flow (low flow time), and exhibitmechanical properties that allow the composite membranes to be preparedand assembled into a filter cartridge or filter product.

Bubble point is an understood property of a porous material, includingof a composite filter membrane as described. Bubble point can correspondto pore size, which may correspond to filtering performance. A smallerpore size can be correlated to a higher bubble point and possibly tohigher filtering performance (higher retention). Normally, however, ahigher bubble point also correlates with relatively higher resistance offlow through a porous material, and a lower flux. According to certainpreferred embodiments, a composite filter membrane can exhibit acombination of a relatively higher bubble point, good filteringperformance, yet still exhibit a good or advantageous flow (relativelyhigh flow rate, or relatively high flux), e.g., a flux that may beassociated with a much lower bubble point in other hollow fiber membranedesigns or compositions.

By one method of determining the bubble point of a porous material, asample of the porous material is immersed in and wetted with a liquidhaving a known surface tension, and a gas pressure is applied to oneside of the sample. The gas pressure is gradually increased. The minimumpressure at which the gas flows through the sample is called a bubblepoint. Examples of useful bubble points of a porous filter membrane asdescribed, measured using ethoxy-nonafluorobutane (HFE 7200) from Novec,IPA, or water, compressed air or compressed N₂ gas, at a temperature offrom 20 to 30 (normally 25) degrees Celsius, can be in a range from 2 to500 psi, e.g., from 50 to 500 psi, from 2 to 400 psi, or from 135 to 185psi.

In combination with a desired bubble point and filtering performance(e.g., measured by retention) a composite membrane as described canexhibit a useful or advantageously low resistance of flow of liquidthrough the composite membrane. A resistance to liquid flow can bemeasured in terms of flux. A composite membrane as described canpreferably have a relatively high flux, preferably in combination with abubble point that is relatively high and good filtering performance. Anexample of a useful or preferred flux can be at least 10 LMH/bar (litersper square meter per hour), e.g., at least 20 LMH/bar, or at least 30LMH/bar or in a range from 20 to 8000 LMH/bar.

A filter membrane as described herein, or a filter or filter componentthat contains a composite hollow fiber filter membrane as described, canbe useful in a method of filtering a liquid chemical material to purifyor remove unwanted materials from the liquid chemical material,especially to produce a highly pure liquid chemical material that isuseful for an industrial process that requires chemical material inputthat has a very high level of purity. Generally, the liquid chemical maybe of any of various useful commercial materials, and may be a liquidchemical that is useful or used in any application, for any industrialor commercial use. Particular examples of filters as described can beused to purifying a liquid chemical that is used or useful in asemiconductor or microelectronic fabrication application, e.g., forfiltering a liquid solvent or other process liquid used in a method ofsemiconductor photolithography. Some specific, non-limiting, examples ofsolvents that can be filtered using a filter membrane as describedinclude: n-butyl acetate (nBA), isopropyl alcohol (IPA), 2-ethoxyethylacetate (2EEA), a xylene, cyclohexanone, ethyl lactate, methyl isobutylcarbinol (MIBC), methyl isobutyl ketone (MIBK), isoamyl acetate,undecane, propylene glycol methyl ether (PGME), propylene glycolmonomethyl ether acetate (PGMEA), or a mixture of any of these, such asmixture of PGME and PGMEA

The composite membrane can be contained within a larger filter structuresuch as a filter or a filter cartridge that is used in a filteringsystem. The filtering system will place the composite filter membrane,e.g., as part of a filter or filter cartridge, in a flow path of aliquid chemical to cause at least a portion of the flow of the liquidchemical to pass through the filter layer of the composite filtermembrane, so that the filter layer removes an amount of the impuritiesor contaminants from the liquid chemical. The structure of a filter orfilter cartridge may include one or more of various additional materialsand structures that support the composite filter membrane within thefilter to cause fluid to flow from a filter inlet, through the compositemembrane (including the filter layer), and thorough a filter outlet,thereby passing through the composite filter membrane when passingthrough the filter.

Examples of useful filters and method for assembling the filters aredescribed in International Patent Application Publication Number WO2017/007683, the entirety of which is incorporated herein by reference.FIGS. 2 and 3 show examples of these filters.

FIGS. 2 and 3 illustrate an example of a fluid separation device orfilter that includes a composite filter membrane of the presentdescription. FIG. 2 is an external view of a filter and FIG. 3illustrates the composite membrane (multiple composite membranes) andthe flow of liquid to be separated as the liquid enters and exits thefluid separation device. The fluid separation device (filter) includeshousing 110 which comprises multiple composite membranes 112. Eachmembrane 112 is potted at each of two opposed both end regions to form afluid tight seal between the end regions and an open middle region 107.Open middle region 107 is not potted and must remain open so thatpermeate 106 can travel through each membrane 112, as discussed below.The potted end regions do not allow liquid to pass through, and aretherefore “fluid-tight.”

In use, a liquid feed enters the housing at active 101, and isintroduced to membranes 112 inside the housing. The membranes 112separate the space within the housing into a first volume 103 and secondvolume 103 b. Upon exposure of the liquid feed to the membranes 112 thepermeate, which is material that passes through the membranes 112,enters the second volume 103 b, and the retentate, the material thatdoes not pass through the membrane 102, enters the first volume. Theretentate can then be collected or filtered further upon extraction fromthe housing via connector 105. The permeate exits via a differentconnector 106, where is can be concentrated, disposed of, orrecirculated back into the system.

In the filter embodiment of FIGS. 2 and 3, a portion of the feed liquidpasses through one of the composite membranes 112 to form the permeate,and another portion of the feed liquid passes through the filter withoutpassing through a composite membrane 112. According to other filterembodiments, the entire amount of feed liquid passes through a compositemembranes 112 to form permeate, and no portion of the feed fluidby-passes the composite membranes 112 to form the retentate. See, forexample, FIG. 6 of U.S. Pat. No. 5,695,702, the entire content of thatpatent document being incorporated herein by reference.

EXAMPLES

Example 1. Fabrication of composite Polyimide (P84)/Nylon hollow fiber.A 0.2 micron Nylon hollow fiber was used as the hollow fiber support. Apolymer solution consisting of P84 polyimide/NMP/propionic acid (17/75/8weight percent) was pumped using a syringe pump with a flow rate of 1ml/min through the annular section of an annular die with the followingdimensions: ID=1 mm, annular region gap=0.3 mm. The extrudate passedthrough an air-gap distance of 1 centimeter before entering acoagulation bath consisting of water. The hollow fiber support drawingspeed through the die was 2 feet per minute.

Example 2. Fabrication of composite polyamide-imide (Torlon)/Nylonhollow fiber. A 0.2 micron Nylon hollow fiber was used as the hollowfiber support. A polymer solution consisting of cured Torlon @275°C./NMP/Triethylene Glycol (12/70/18 wt%) was pumped using a syringe pumpwith a flow rate of 1 ml/min through the annular section of an annulardie with the following dimensions: ID=1 mm, annular region gap=0.3 mm.The extrudate passed through an air-gap distance of 1 centimeter beforeentering a coagulation bath consisting of water. The hollow fiberdrawing speed through the die was 2 ft/min.

In a first aspect, a composite hollow fiber filter membrane comprises: apolymeric, microporous, hollow fiber support comprising: an outersurface, an inner surface, a thickness extending between the outersurface and the inner surface, and micropores; and a porous polymericfilter layer comprising coagulated polymer contacting the outer surface.

A second aspect according to the first aspect, wherein the filter layerincludes pores having an average pore size that is smaller than anaverage pore size of the micropores of the hollow fiber support.

A third aspect according to the first or second aspect, wherein thehollow fiber support has an average pore size of less than 10 microns.

A fourth aspect according to the third aspect, wherein the filter layerhas an average pore size in a range from 1 nanometer to 8 microns.

A fifth aspect according to any of the preceding aspects, wherein thehollow fiber support (in the absence of the filter layer) has athickness in a range from 20 to 200 microns.

A sixth aspect according to any of the preceding aspects, wherein thehollow fiber support comprises, consists of, or consists essentially ofone or a combination of polyolefin and nylon.

A seventh aspect according to any of the preceding aspects, wherein thefilter layer penetrates the thickness of the hollow fiber support to adepth of not greater than 2 microns.

An eighth aspect according to any of the preceding aspects, wherein thecoagulated polymer is formed by immersion precipitation of filter layerpolymer on the hollow fiber support.

A ninth aspect according to any of the preceding aspects, wherein thefilter layer comprises polymer that is soluble in solvent selected fromthe group consisting of n-methyl pyrrolidone (NMP), dimethylformamide(DMF), dimethylacetamide (DMAc), and combinations thereof.

A tenth aspect according to any of the preceding aspects, wherein thefilter layer is resistant to solvent selected from the group consistingof propylene glycol methyl ether (PGME), propylene glycol methyletheracetate (PGMEA), and cyclohexanone.

An eleventh aspect according to any of the preceding aspects, whereinthe coagulated polymer comprises polymer selected from the groupconsisting of polyimide, polyamide-imide, and polyamide.

A twelfth aspect according to any of the preceding aspects, wherein thecomposite membrane has a flux in a range from 20 to 8000 LMH/bar andbubble point in a range from 50-500 psi measured usingethoxy-nonafluorobutane (HFE 7200) at a temperature of 25 degreesCelsius.

A thirteenth aspect according to any of the preceding aspects, whereinthe porous polymeric filter layer penetrates not more than partiallyinto the thickness of the hollow fiber support.

A fourteenth aspect according to any of the first through twelfthaspects, wherein the porous polymeric filter layer penetratessubstantially into the thickness of the hollow fiber support.

A fifteenth aspect according to any of the preceding aspects, whereinthe filter layer includes pores having an average pore size that islarger than an average pore size of the micropores of the hollow fibersupport.

In a sixteenth aspect, a filter comprises the composite hollow fiberfilter membrane of any of the first through fifteenth aspects.

In a seventeenth aspect, a method of filtering a fluid comprises:passing fluid through a filter according to the sixteenth aspect bypassing the fluid in a direction of flow through the filter layer firstand through the hollow fiber support second.

An eighteenth aspect according to the seventeenth aspect, wherein thefluid is a semiconductor lithography solvent.

A nineteenth aspect according to the eighteenth aspect, wherein thesolvent is selected from the group consisting of propylene glycol methylether (PGME), propylene glycol methylether acetate (PGMEA),cyclohexanone, and n-butyl acetate.

A twentieth aspect according to the seventeenth aspect, wherein thesolvent is selected from dilute or concentrated hydrofluoric acid,sulfuric acid, and a peroxide solution.

In a twenty-first aspect, includes a method of preparing a compositehollow fiber filter membrane comprising a polymeric, microporous, hollowfiber support and a porous polymeric filter layer, the methodcomprising: placing a polymer solution coating on an outer surface ofthe polymeric, microporous, hollow fiber support, the polymer solutioncomprising polymer dissolved in solvent, and contacting the polymersolution coating with coagulation solution to cause dissolved polymer ofthe polymer solution coating to form a layer of coagulated polymer onthe outer surface, the layer of coagulated polymer contacting the outersurface and penetrating not more than partially into a thickness of thepolymeric, microporous, hollow fiber support.

A twenty-second aspect according to the twenty-first aspect, furthercomprising, during placing: passing the polymeric, microporous, hollowfiber support through a central opening of an annular die, and passingthe polymer solution through an annular opening of the annular die toplace the polymer solution coating on the outer surface.

A twenty-third aspect according to the twenty-first aspect or thetwenty-second aspect, further comprising allowing for an amount ofevaporation of the polymer solution coating before contacting thepolymer solution coating with the coagulation solution.

A twenty-fourth aspect according to any of the twenty-first throughtwenty-third aspects, wherein the coagulated polymer comprises polymerselected from the group consisting of polyimide, polyamide-imide, andpolyamide.

A twenty-fifth aspect according to any of the twenty-first throughtwenty-fourth aspects, wherein the hollow fiber support comprises,consists of, or consists essentially of polyolefin or nylon.

1. A composite hollow fiber filter membrane comprising: a polymeric,microporous, hollow fiber support comprising: an outer surface, an innersurface, a thickness extending between the outer surface and the innersurface, and micropores; and a porous polymeric filter layer comprisingcoagulated polymer contacting the outer surface.
 2. The compositemembrane of claim 1, wherein the filter layer includes pores having anaverage pore size that is smaller than an average pore size of themicropores of the hollow fiber support.
 3. The composite membrane ofclaim 1, wherein the hollow fiber support has an average pore size ofless than 10 microns.
 4. The composite membrane of claim 3, wherein thefilter layer has an average pore size in a range from 1 nanometer to 8microns.
 5. The composite membrane of claim 1, wherein the hollow fibersupport (in the absence of the filter layer) has a thickness in a rangefrom 20 to 200 microns.
 6. The composite membrane of claim 1, whereinthe hollow fiber support comprises polyolefin or nylon.
 7. The compositemembrane of claim 1, wherein the filter layer penetrates the thicknessof the hollow fiber support to a depth of not greater than 2 microns. 8.The composite membrane of claim 1, wherein the coagulated polymer isformed by immersion precipitation of filter layer polymer on the hollowfiber support.
 9. The composite membrane of claim 1, wherein the filterlayer comprises polymer that is soluble in solvent selected from thegroup consisting of n-methyl pyrrolidone (NMP), dimethylformamide (DMF),dimethylacetamide (DMAc), and combinations thereof
 10. The compositemembrane of claim 1, wherein the filter layer is resistant to solventselected from the group consisting of propylene glycol methyl ether(PGME), propylene glycol methylether acetate (PGMEA), and cyclohexanone.11. The composite membrane of claim 1, wherein the coagulated polymercomprises polymer selected from the group consisting of polyimide,polyamide-imide, and polyamide.
 12. The composite membrane of claim 1,wherein the composite membrane has a flux in a range from 20 to 8000LMH/bar and bubble point in a range from 50-500 psi measured usingethoxy-nonafluorobutane (HFE 7200) at a temperature of 25 degreesCelsius.
 13. The composite membrane of claim 1, wherein the porouspolymeric filter layer penetrates not more than partially into thethickness of the hollow fiber support.
 14. The composite membrane ofclaim 1, wherein the porous polymeric filter layer penetratessubstantially into the thickness of the hollow fiber support.
 15. Thecomposite membrane of claim 1, wherein the filter layer includes poreshaving an average pore size that is larger than an average pore size ofthe micropores of the hollow fiber support.
 16. A method of preparing acomposite hollow fiber filter membrane comprising a polymeric,microporous, hollow fiber support and a porous polymeric filter layer,the method comprising: placing a polymer solution coating on an outersurface of the polymeric, microporous, hollow fiber support, the polymersolution comprising polymer dissolved in solvent, and contacting thepolymer solution coating with coagulation solution to cause dissolvedpolymer of the polymer solution coating to form a layer of coagulatedpolymer on the outer surface, the layer of coagulated polymer contactingthe outer surface and penetrating not more than partially into athickness of the polymeric, microporous, hollow fiber support.
 17. Themethod of claim 16 further comprising, during placing: passing thepolymeric, microporous, hollow fiber support through a central openingof an annular die, and passing the polymer solution through an annularopening of the annular die to place the polymer solution coating on theouter surface.
 18. The method of claim 16, further comprising allowingfor an amount of evaporation of the polymer solution coating beforecontacting the polymer solution coating with the coagulation solution.19. The method of claim 16, wherein the coagulated polymer comprisespolymer selected from the group consisting of polyimide,polyamide-imide, and polyamide.
 20. A filter comprising a compositehollow fiber filter membrane comprising: a polymeric, microporous,hollow fiber support comprising: an outer surface, an inner surface, athickness extending between the outer surface and the inner surface, andmicropores; and a porous polymeric filter layer comprising coagulatedpolymer contacting the outer surface.